#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
	float  a, b, c,t1,t2,t;
	scanf("%f%f%f%f", &a, &b, &c,&t1);
	float ago = (1.0 / a + 1.0 / b) * t1;
	float d = 1.0 / a;
	float e = 1.0 / b;
	float f = 1.0 / c;
	t2= (1.0 - ago) / (d + e - f);
	t = t1 + t2;
	printf("%.2f",t);
	return 0;
}